This invention relates to a control system for hydraulically driven vehicles and in particular to a control system in which the displacement of a variable displacement hydraulic motor is automatically changed in response to a higher fluid pressure at both ports thereof.
A hydraulically driven vehicle generally includes a pair of variable displacement hydraulic pumps each driven by a common engine and a pair of variable displacement hydraulic motors each connected with the respective pumps in a closed loop and driven thereby. A control system has been known for such a hydraulically driven vehicle in which vehicle speed can be varied in two stages by controlling the angle of each swash plate of the respective motors by regulators.
In this system, however, because fluid which operates the regulators is introduced therein from a conduit on the upstream side of a brake valve disposed in the respective closed loops, it is difficult to obtain enough braking force when the vehicle is to be stopped since the variable displacement hydraulic motors are changed over to their low displacement positions at that time.